Some recently image forming apparatuses, including copiers, printers, multifunction peripherals, perform calibration at predetermined times in order to maintain image quality of printed matter. Heretofore there have been various kinds of calibration techniques. For example, Japanese Unexamined Patent Application Publication No. H10(1998)-304217 (PTL 1) discloses an image processing apparatus that when calibration is needed in the process of continuous printing, suspends the printing operation to perform calibration and resumes the printing operation afterward. Japanese Unexamined Patent Application Publication No. 2000-190573 (PTL 2) discloses a print system that does not perform calibration if the system determines that a print job includes a calibration stop command.
Japanese Unexamined Patent Application Publication No. 2005-132030 (PTL 3) discloses a color printing apparatus that performs calibration concurrently with print data processing, but aborts the calibration if it is unnecessary. Japanese Unexamined Patent Application Publication No. 2006-62279 (PTL 4) discloses an image forming apparatus that when receiving a print command during calibration, allows users to selectively assign priority to the calibration or the print command. In addition, Japanese Unexamined Patent Application Publication No. 2006-293141 (PTL 5) discloses an image forming apparatus that sets an optimal toner ejection mode to be used in a refresh process performed to refresh toner on a developing roller according to users' usage.
By the way, recent technological advances have developed apparatuses for measuring users' biological signals. For example, Japanese Translation of PCT International Application Publication No. 2008-526367 (PTL 6) discloses a portable vital signs measurement instrument that provides a variety of measurement capabilities to indicate patient conditions, such as blood pressure, temperature, and pulse oximetry.